Positive Displacement Carbon Dioxide Expansion Machines - Chances and Limitations

摘要

Over the past years carbon dioxide has experienced a revival after it had been re-introduced by Lorentzen. In contrast to conventional refrigeration cycles the expansion of CO_2 in refrigeration machines is a potential source of energy efficiency improvement, when the expansion energy can be put to practical use. Various efforts to realize expanders for CO_2 have been reported at Purdue and IIR conferences.rnAt FKW a simple reciprocating CO_2 expansion machine without special valve- or slot-control has been studied as previously designed by Doll and Eder for cryogenic helium expansion |7|. This simple kind of charge and discharge control works without any additional control components except the piston and allows also dead volume capacity control.rnWith a flexible simulation program for expansion machines thermodynamic calculations were done. The results of these calculations and the design of the machine will be described and discussed in the presentation as well as experimental investigations concerning the gained work both in transcritical two-phase operation and in the superheated single-phase region at comparable pressures.rnFrom these results conclusions will be drawn concerning the chances and limitations of the application of positive displacement expansion machines of the reciprocating and rotating types.